TY - JOUR
T1 - Derivatives of the[Ru(bipy)(CN)4]2- chromophore with pendant pyridyl-based binding sites
T2 - Synthesis, pH dependent-luminescence, and time-resolved infrared spectroscopic studies
AU - Encinas, S.
AU - Morales, A. F.
AU - Barigelletti, F.
AU - Barthram, A. M.
AU - White, C. M.
AU - Couchman, S. M.
AU - Jeffery, J. C.
AU - Ward, M. D.
AU - Grills, D. C.
AU - George, M. W.
N1 - Copyright:
Copyright 2009 Elsevier B.V., All rights reserved.
PY - 2001
Y1 - 2001
N2 - Reaction of K4[Ru(CN)6] with 2,2′:4′ ,4″-terpyridine (L1) or 2,2′:3′ ,2″:6″ ,2‴-quaterpyridine (L2) in acidic aqueous methanol affords the complexes K2[Ru(L1)(CN)4] and K2[Ru(L2)(CN)4] respectively, both containing the {Ru(bipy)(CN)4}2- chromophore but with pendant pyridyl or bipyridil units, respectively. Time-resolved IR analysis of K2[Ru(CN)4(L2)] in MeCN-D2O showed that the most intense CN stretching vibration shifted to higher energy by ca. 50 cm-1 after laser excitation, consistent with formation of a Ru(III)/(L2)·- MLCT excited state for which the lifetime measurement (38 ± 5 ns, measured by TRIR) agrees reasonably well with the value measured by luminescence methods (30 ± 2 ns). Study of the pH dependence of the absorption and emission spectra of the two complexes revealed the presence of two different effects arising from protonation of the pendant pyridyl/bipyridyl site (which occurs with pKa ≈ 3.1 in each case) and protonation of the cyanide ligands (which occurs with pKa ≈ 2 in each case). For K2[Ru(L1)(CN)4], protonation of the pendant pyridyl unit results in the 1MLCT excited state being lowered in energy by ca. 1000 cm-1, whereas at lower pH values (2.5-1), protonation of the cyanide ligands raises the 1MLCT excited state energy by over 2000 cm-1. For K2[Ru(L2)(CN)4] in contrast, protonation of the pendant bipyridyl unit has no detectable effect on the 1MLCT energy, as the pendant site is electronically decoupled from the complex core by a substantial twist between the free and coordinated bipy components of L2; protonation of the cyanides at lower pH values however destabilises the 1MLCT excited state. Protonation of the pendant pyridyl sites results in complete (for [Ru(L1(CN)4]2-) or near-complete (for [Ru(L2)(CN)4]2-) quenching of the luminescence; possible reasons for this behaviour are discussed. The crystal structures of the two related complexes [Ru(tBu2bipy)2(L1)][PF 6]2 and [Cl2Pt(μ-L2)Ru(bipy)2][PF6] 2 are also described to illustrate arguments about the conformations of L1 and L2.
AB - Reaction of K4[Ru(CN)6] with 2,2′:4′ ,4″-terpyridine (L1) or 2,2′:3′ ,2″:6″ ,2‴-quaterpyridine (L2) in acidic aqueous methanol affords the complexes K2[Ru(L1)(CN)4] and K2[Ru(L2)(CN)4] respectively, both containing the {Ru(bipy)(CN)4}2- chromophore but with pendant pyridyl or bipyridil units, respectively. Time-resolved IR analysis of K2[Ru(CN)4(L2)] in MeCN-D2O showed that the most intense CN stretching vibration shifted to higher energy by ca. 50 cm-1 after laser excitation, consistent with formation of a Ru(III)/(L2)·- MLCT excited state for which the lifetime measurement (38 ± 5 ns, measured by TRIR) agrees reasonably well with the value measured by luminescence methods (30 ± 2 ns). Study of the pH dependence of the absorption and emission spectra of the two complexes revealed the presence of two different effects arising from protonation of the pendant pyridyl/bipyridyl site (which occurs with pKa ≈ 3.1 in each case) and protonation of the cyanide ligands (which occurs with pKa ≈ 2 in each case). For K2[Ru(L1)(CN)4], protonation of the pendant pyridyl unit results in the 1MLCT excited state being lowered in energy by ca. 1000 cm-1, whereas at lower pH values (2.5-1), protonation of the cyanide ligands raises the 1MLCT excited state energy by over 2000 cm-1. For K2[Ru(L2)(CN)4] in contrast, protonation of the pendant bipyridyl unit has no detectable effect on the 1MLCT energy, as the pendant site is electronically decoupled from the complex core by a substantial twist between the free and coordinated bipy components of L2; protonation of the cyanides at lower pH values however destabilises the 1MLCT excited state. Protonation of the pendant pyridyl sites results in complete (for [Ru(L1(CN)4]2-) or near-complete (for [Ru(L2)(CN)4]2-) quenching of the luminescence; possible reasons for this behaviour are discussed. The crystal structures of the two related complexes [Ru(tBu2bipy)2(L1)][PF 6]2 and [Cl2Pt(μ-L2)Ru(bipy)2][PF6] 2 are also described to illustrate arguments about the conformations of L1 and L2.
UR - http://www.scopus.com/inward/record.url?scp=0034746853&partnerID=8YFLogxK
M3 - Article
AN - SCOPUS:0034746853
SN - 1470-479X
SP - 3312
EP - 3319
JO - Journal of the Chemical Society. Dalton Transactions
JF - Journal of the Chemical Society. Dalton Transactions
IS - 22
ER -